This invention relates to certain biscyclopentadienyl Group 4 transition metal complexes possessing diene ligands and to polymerization catalysts obtained from such. In one form this invention relates to biscyclopentadienyl and substituted bis(cyclopentadienyl)titanium, zirconium or hafnium complexes possessing diene ligands in which the metal is either in the +2 or +4 formal oxidation state which can be activated to form catalysts for the polymerization of olefins and to methods for preparing such complexes and catalysts.
The preparation and characterization of certain biscyclopentadienyl (Cp.sub.2) zirconium and hafnium diene complexes is described in the following references: Yasuda, et al., Organometallics, 1982, 1, 388 (Yasuda I); Yasuda, et al. Acc. Chem. Res., 1985, 18 120 (Yasuda II); Erker, et al., Adv. Organomet. Chem., 1985, 24, 1 (Erker I); Erker et al. Chem. Ber., 1994, 127, 805 (Erker II); and U.S. Pat. No. 5,198,401. The last reference describes the use of Cp.sub.2 Zr(diene) where the Zr is in the +4 formal oxidation state as an olefin polymerization catalyst in combination with ammonium borate cocatalysts.
Biscyclopentadienyl Group 4 transition metal complexes in which the metal is in the +4 formal oxidation state, and olefin polymerization catalysts formed from such complexes by combination with an activating agent, e.g., alumoxane or ammonium borate, are known in the art. Thus, U.S. Pat. No. 3,242,099 describes the formation of olefin polymerization catalysts by the combination of biscyclopentadienyl metal dihalides with alumoxane. U.S. Pat. No. 5,198,401 discloses tetravalent biscyclopentadienyl Group 4 transition metal complexes and olefin polymerization catalysts obtained by converting such complexes into cationic form in combination with a non-coordinating anion. Particularly preferred catalysts are obtained by the combination of ammonium borate salts with the biscyclopentadienyl titanium, zirconium or hafnium complexes. Among the many suitable complexes disclosed are bis(cyclopentadienyl)zirconium complexes containing a diene ligand attached to the transition metal through .sigma.-bonds where the transition metal is in its highest (+4) formal oxidation state.
Copending applications, Ser. No. 08/082,197 filed Jun. 24, 1993, Ser. No. 08/230,051 filed Apr. 19, 1994 and Ser. No. 08/241,523 filed May 12, 1994 disclose monocyclopentadienyl diene complexes with titanium or zirconium in which the metal is in the +2 formal oxidation state and the formation of olefin polymerization catalysts from such complexes by the combination of the complex with activator compounds such as alumoxane, ammonium borate salts or strong Lewis acids such as tris(pentafluorophenyl)borane capable of converting the complexes to active forms.
The present invention provides novel olefin polymerization catalysts which can be employed over a wide range of physical conditions and with a wide range of olefin monomers and combinations of such monomers, thus providing an outstanding opportunity of tailor making polyolefins having specifically desired properties.